Active matrix display devices such as liquid crystal display devices and organic electroluminescent (EL) display devices widely use thin-film transistors (TFTs) as switching elements or driver elements.
In recent years, active research and development have been conducted on structures that include an oxide semiconductor such as zinc oxide (ZnO), indium gallium oxide (InGaO), or indium gallium zinc oxide (InGaZnO) as channel layers of TFTs. The TFTs including the oxide semiconductor as their channel layers are characterized by having a small off-state current, exhibiting high carrier mobility even in an amorphous state, and being able to be formed by a low-temperature process.
Techniques for supplying oxygen to oxide semiconductor layers of TFTs to reduce degradation of electrical characteristics have conventionally been disclosed. For example, PTL 1 discloses a technique for performing heat treatment on an oxide semiconductor layer after formation of the oxide semiconductor layer to supply oxygen to the oxide semiconductor layer.